Nuclear reactor control means



March 14, 1967 J.J. DICKSON NUCLEAR REACTOR CONTROL MEANS 5 Sheets-Sheet.1

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United States Patent 3,309,278 NUCLEAR REACTOR CONTROL MEANS James J.Dickson, Silver Spring, Md., assignor to Allis- Chalmers ManufacturingCompany, Milwaukee, Wis. Original application Jan. 5, 1961, Ser. No.80,774, now

Patent No. 3,208,914, dated Sept. 28, 1965. Divided and this applicationNov. 24, 1964, Ser. No. 419,625

1 Claim. (Cl. 176-36) This is a division of application Ser. No. 80,774,filed Jan. 5, 1961, now Patent No. 3,208,914.

This invention relates to nuclear reactors, and more particularly topower reactors which are adapted for use in mobile units as a source ofpropelling power.

Various types of neutronic reactors including pressurized water as wellas boiling water and gas cooled (graphite moderated) types haveheretofore been proposed for use in self-propelled units. However, theprovision of an atomic power plant for mobile units which issatisfactory not only in its technical but also in its various practicalaspects presents problems, diflculties and requirements which arepeculiar to the environmental and operational conditions of the unit andwhich are not ordinarily encountered in land based stationary or fixedsite installations.

For instance, in the conventional fixed site installation of watercooled and moderated reactors the react-or vessel and core are normallyset up in a vertical position, the control rods are moved axially of thecore, shielding is placed not only around the reactor vessel but alsoabove and below it, and the actuating mechanism for the control rods islocated generally at one end of the reactor vessel. Such an arrangementof the reactor complex in a stationary installation presents noparticular problems in terms of operability, installed or total cost ofthe reactor complex, or in accessibility of reactor components forinspection, repair, outrage and overhaul. However, in mobile units andin submarines in particular, the conventional vertical arrangement ofthe reactor entails considerable difliculties due to prevailingenvironmental and Specifically, in a submarine, the use of reactors withhigh head room determines the diameter of the pressure hull and hencethe silhouette which in turn governs its relative detectability assubmerged. The load concentration of the conventional high head reactor,with its heavy shielding also does not allow distribution of loads inthe hull to avoid areas of high stress concentration. The metacenter ofthe vessel cannot be kept as high as would be desirable because of therelatively high location of the center of gravity of the verticallypositioned reactor complex.

A further disadvantage of the conventional vertical reactor arrangementin a submarine is the requirement of fuel withdrawal through aconsiderable distance from the core to the transfer or shipping caskemployed as a protective container. This installing or removal distancegives manipulative difficulties in groping for and attachment of fuelelements.

Another difliculty which is characteristic of the use of verticalreactors in self-propelled units, and particularly in submarines, arisesfrom the change of inclination from the vertical to which the react-orbecomes subjected in such use and which, in a submarine, may involvevery steep angles fore and aft in dive and surfacing operations. Rolland pitch of the vessel in heavy seas while floating, diving orsurfacing must also be anticipated. These conditions affect thegravitational forces on the moving and movable parts of the reactorsystem as well as the water and steam separation. They may also causeshifting of the water level in the reactor vessel and thereby create adanger of momentary excessive radiation.

Generally, it is an object of the invention to provide an improvednuclear reactor which lends itself to use as a power source for mobileunits and which will take care of the mentioned and other difficultiesand requirements of such use in a practical and entirely satisfactorymanner.

A further object of the invention is to provide an improved nuclearreactor of the above outlined character wherein control rods are movableaxially of the vessel to different positions of adjustment including ascram position, various regulating positions, and a core unloadingposition wherein the control portions of the rods are entirely withdrawnfrom the active core region to facilitate installation of the fuelelements within and their removal from the reactor vessel through thementioned top opening.

A further object of the invention is to provide an improved mechanismfor actuating the control rods of a nuclear reactor of the abovementioned character, the mechanism being operable by one power source,such as an electric motor, to adjust a control rod or rods to variousregulating positions, and by another power source such as a pneumaticcylinder, to actuate the control rods to scram positions.- Adjustment ofthe control rods to the mentioned core unloading positions is preferablyeffected by means of the same power source which adjusts the controlrods to their regulating positions.

These and other objects and advantages are attained by the presentinvention, various novel features of which will be apparent from thedescription herein and the accompanying drawings disclosing anembodiment of the invention, and will be more particularly pointed outin the appended claim.

Referring to the drawings:

FIG. 1 is an elevational side view of a mobile nuclear reactor andenvironmental structure, part of the reactor and environmental structurebeing broken away and shown in section;

FIG. 2 is an enlarged section taken along line IIII of FIG. 1, part ofthe environmental structure being broken away;

FIG. 3 is an enlarged and more detailed section of the reactor shown inFIG. 1;

FIG. 4 is an enlarged isometric schematic view of part of the reactorcontrol mechanism; and

FIGS. 5, 6 and 7 are diagrammatic views illustrating various conditionsof adjustment of the control mechanism shown in FIG. 7.

Referring to FIG. 1, a reactor pressure vessel 10 is a horizontallydisposed vessel which is closed at one end and open at the other andwhich has an autwardly extending flange 20 around its open end. Thereactor has an access opening 21 which serves as a refueling port in anupper longitudinally extending side wall of the vessel 10, a refuelingport cover 22, an end head 23, an end head cover 24 and coolant inletand outlet ports 25, 26.

The end head 23 comprises a longitudinally extending tubular housing 27having outwardly extending flanges 28, 29 at its ends, respectively, andforms a coaxial extension to vessel 10. Housing flange 28 abuts thevessel flange 20 and is attached thereto by means such as bolts 30. Acover 24 is attached to the other housing flange 29 by means such asbolts 32.

To provide adequate sealing, suitable gaskets (not shown) are disposedbetween flange 29 and cover 24 and flanges 20, 28, and light seal weldsare made around the outer periphery of the joint between the flanges 20,28 and the flange 29 and cover 24.

The end head 23 has three bores 33 defined therethrough transverse tothe axis thereof for passage of three control rod drive shafts 34, onlyone of these bores and shafts being shown. Upward extending adapters 35are disposed concentrically within the bores 33 and provide means forconnecting the control rod drives 36.

Nuclear core 12 is centrally disposed in vessel 10 and comprises ashroud structure 55 having a compact stacked arrangement of coreelements therein, the core elements include sixty fuel elementassemblies 51, 51', six dummy fuel assemblies 52, nine control rodassemblies 47 and nine guide sleeves 53.

Shroud 55, having side and bottom portions 56, 57, is supported at eachend by front and rear end plates 58, 59 (FIG. 3) that rest on front andrear rings 60, 61 (FIG. 3) attached to the shell of vessel 10 as bywelding. The rear end plate 59 is fixed to rear ring 61 and the frontend plate 58 (FIG. 3) is slidably mounted on front ring 60 toaccommodate thermal expansion. The end plates 58, 59 have flow openings62 defined therethrough and guide tube extensions 63, 64 extendingtherefrom to receive the reciprocable sections 65, 66 of each controlrod assembly 47. Shroud 55 is open at the top to allow the core elementsto be removed and replaced through the refueling port 21. A handlingdevice such as grappling tool 90 shown in FIG. 3 and describedhereinafter is provided to remove and replace the individual coreelements.

The control rod guide sleeves 53 are removable in the same Way as thefuel assemblies 51, 51 and have substantially the same circumferentialdimensions as the fuel assemblies 51, 51', but are slightly longer thanthe latter.

The core is controlled in conventional fashion by nine control rodassemblies 47 in a three times three array around the core center line.The reactor power is adjusted by endwise movement of the rods 47 betweena scram position (FIG. and an operating position (FIG. 6). The depletionof the burnable boron, if utilized, also adjusts the amount of availablefission material. The control rods 47 are of square cross sectionalconfiguration and are dimensioned to fit the space within the guide tube53. Each rod assembly 47 comprises three detachably interconnectedsections; namely, a fuel section 65, a poison section 66 and a racksection 48.

As shown in FIG. 4, the control rod assemblies 47 are sequentiallyassembled in an end to end relationship by coupling means utilizing adovetail arrangement at the ends of the sections. The rack section 48 isprovided with a T-slot 86; the fuel section 65 is provided with a T-slot87 at one end thereof; and the poison section 66 is provided withT-heads 88 at its opposite ends. To assemble the control rod assembly47, only the poison section 66 can be coupled to the rack section 48,and the fuel section 65 can only be coupled to the poison section 66.This arrangement prevents accidental coupling of the fuel section 65directly to the rack section which would dispose a fuel section 65 inthe core geometry during a scram.

As shown in FIGS. 1, 2 and 3, control rod drive mechanism 36 isremovably mounted above vessel and is supported on the tubular housing27 by adapter 35. Shaft 34 (FIGS. 3 and 4) depending downward from eachdrive mechanism 36 through the adapter 35 is provided with three piniongears 93 to engage each rack 48. The drive mechanism 36 includes anelectric gear motor 92, magnetic clutch 94, gear box 96, rod positionindicator (not shown), limit switches (not shown), and a pneumaticcylinder 95 for fast scrams. The magnetic clutch 94 transmits torquefrom the drive motor 92 to the gear box 96 when energized and isdisposed between the drive motor 92 and gear box 96. The pneumatic scramcylinder 95 is disposed on a level below gear box 96 and is operativelycoupled to drive shaft 34 during a scram. The scram mechanism is failsafe; that is, a loss in power deenergizes the magnetic clutch 94 todisconnect the electric motor 92 from the gear box 96 and permits thepneumatic cylinder 95 to drive the fuel section 65 of the control rodassembly 47 out of the core lattice and simultaneously substitute thepoison section 66.

During normal reactor operation both ends of the pneumatic scramcylinder are vented through a three-Way, spring loaded solenoid valve(not shown) so that the cylinder plunger 97 freely follows the pinionshaft 34.

The plunger 97 is provided with a racklike extension 111 (FIG. 4). Ascram pinion 112 is slip mounted on drive shaft 34 and is in engagementwith rack 111. A jaw clutch 113 is associated with scram pinion 112 toalternatively engage pinion 112 to and disengage pinion 112 from shaft34. During reactor operation, jaw clutch 113 is actuated to maintainpinion 112 in engagement with shaft 34. Thus, in the event of a scram,the movement of the plunger extension 111 is transmitted to the piniongear and hence causes the shaft 34 to move the poison sections of thecontrol rod assemblies 47 into the core 12.

Upon a scram signal, the magnetic clutch 94 and the solenoid valve (notshown) are deenergized. The valve is automatically positioned to directcompressed air into the cylinder 95 through pipe 98 and drive theplunger 97 to the scram position (FIG. 5). A dashpot (not shown) may beprovided in the cylinder 95 to absorb the impact of the plunger 97 atscram velocity. It is equally possible to use spring loaded solenoidvalves to control the flow of air through pipes 98 and 99, respectively,into and out of the scram cylinder 95.

Three control rod drive mechanisms 36 are provided and are arranged sothat each mechanism 36 drives a gang of three control rod assemblies 47.Each of the three pinion gears 93 (FIG. 4) utilized to drive the threeracks 48 includes a two-way slip clutch (not shown) to permit any rod 47in a gang of three to be operated if one or two become inoperable. Ifdesired, the drive mechanism 36 may be adapted to operate with standbybattery power in event the main power source is interrupted.

To provide adequate circulation of coolant through the core, the fuelassemblies 51, 51 are open at the ends thereof, the guide sleeveextensions 63, 64 are provided with apertures 84 (FIG. 3) at the endsthereof, and each control assembly 47 (FIG. 4) has apertures 89 definedin the ends of each section therein.

It is understood that this invention is not to be limited to the detailsgiven herein, but that it may be modified within the scope of theappended claim.

What is claimed is:

In a nuclear reactor of the type having a core including fuel elementassemblies and a plurality of control rods reciprocable endwise relativeto said fuel element assemblies, a mechanism for simultaneously moving aplurality of said control rods to predetermined positions to endwiseadjustment, said mechanism comprising a plurality of gear racks fixedlyconnected in lengthwise extending relation with said control rods,respectively; a cross shaft rotatably mounted to extend transversely ofsaid gear racks and having a plurality of axially spaced drive pinionssecured thereto in meshing engagement, respectively, with said racks; anauxiliary drive pinion mounted on said shaft in torque transmittingrelation thereto; an auxiliary reciprocable gear rack in mesh with saidauxiliary drive pinion, torque transmitting means connected with saidshaft and operable to selectively rotate the latter in oppositedirections; and thrust transmitting means operatively connected withsaid auxiliary gear rack for moving the latter endwise from onepredetermined position to another.-

References Cited by the Examiner UNITED STATES PATENTS 2,816,860 12/1957Wilson et al. 176-36 2,938,847 5/1960 Yeomans 176-36 3,245,879 4/1966Purdy et al 17636 CARL D. QUARFORTH, Primary Examiner.

L. DEWAYNE RUTLEDGE, Examiner.

H. E. BEHREND, Assistant Examiner.

